That's a pretty strange occurrence. I would expect the oil slopping around in there would lubricate it. If you have a borescope camera, you could take a peek in the socket. I would test fit the next distributor with the camshaft out to see how it's fitting. Grab the gear and move it up, down, left, right, to see if there is excessive play in the socket or distributor shaft. Here is a schematic of the oiling system from the online manual.
http://www.cygnusx1.net/Supra/Librar....aspx?S=LU&P=2
After you get the replacement camshaft installed, insert the distributor by the manual method. It should slide in or out without binding. Aim for the center of the bolt slot while inserting with the alignments set per the method.
http://www.cygnusx1.net/Supra/Librar...aspx?S=IG&P=17